Semiconductor processing apparatus such as, for example, vertical batch furnaces, are known in the art. A single semiconductor processing apparatus may normally be configured to perform one specific treatment step, e.g. oxidation, annealing or chemical vapor deposition, on a single flat substrate or a batch of flat substrates. Since various consecutive treatments may be required to fully process a single substrate, a semiconductor fabrication facility may have multiple semiconductor processing apparatus, each of which may be configured to perform one of the desired treatment steps. Substrates may be transferred between the different semiconductor processing apparatus in a substrate cassette or pod, which may hold a plurality of substrates in a protective, possibly sealed environment. Pods are standardized and therefore attachable to tools from different vendors. Although transporting substrates between tools by means of pods is a tried method, the routine is relatively slow and labor-intensive. Furthermore, for some series of treatments it would be beneficial if substrates could be transferred from one tool to another without breaking or changing the protective ambient around them.
Inter alia to reduce the labor-intensive use of pods, to increase the overall substrate throughput and to improve the quality of composite treatments, attempts have been made to design scalable tools, i.e. tools in which a number of different processing units may be combined, and in which the number and type of the processing units may be changed freely to accommodate to a change in the series of treatments that define the overall fabrication process. Many such attempts, however, have required major concessions in the design of the individual processing units, impairing their competitiveness as stand-alone units or their ability to operate independently. Other attempts have resulted in overly complex and therefore relatively expensive and unreliable designs. An example of a modular semiconductor processing apparatus of the latter type is disclosed by U.S. Pat. No. 4,824,309 (Kakehi et al.).